When the quantity of the gaseous working medium flowing in a closed-cycle gas turbine system is controlled there takes place solely a proportional change in gas pressures at various locations within the circulation system while the aerodynamic and thermodynamic conditions remain constant for all practical purposes. The mechanical efficiency of the system will therefore retain its designed magnitude over a wide range of power load. This type of gas quantity control represents for this reason the primary method of regulating closed-cycle gas turbine systems. Any improvement and simplification of the various components necessary for performing the gas quantity control is therefor desirous and advantageous.
It is immaterial for gradual changes in power output of a closed-cycle type of gas turbine system whether gaseous working medium is added or removed, respectively at the high-pressure side or the low-pressure side of the gas circulating system. An intermediate pressure storage in cascade connection, as illustrated in FIG. 1, is particularly suitable for changing the output within a maximum and a specifically set minimum value when using a filling gas quantity control mode of operation.
In order to accomplish a reduction in load, gas storage tanks S.sub.1 to S.sub.n as in FIG. 1 can be charged in succession by means of valve controls, with the gaseous working medium being removed from the system at the output side of the compressor V.
In order to accomplish an increase in the power output of the turbo-machine group, gaseous working medium can be returned to the system at the low-pressure side, e.g., at the inlet side to the compressor. The tanks S.sub.1 to S.sub.n will then discharge the gas, again in succession until the pressure is equalized as desired.
In order to attain a rapid increase in load, the so-called load surges, it is necessary to inject the gas into the system at a point of higher pressure, at the earliest between two serially connected compressor sections V.sub.1, V.sub.2, (FIG. 2) and a neutral transitory attitude can then be attained only when the second compressor section V.sub.2 has a pressure ratio that is not higher than the pressure ratio of the first compressor section V.sub.1.
When gases possessing great isentropic exponents are utilized, the optimum pressure ratios for closed-cycle turbo-machine groups operating with a recuperator in the circuit will be small so that the storage tanks described above will have a relatively small effective pressure head only.
Another arrangement for controlling the quantity of the gaseous working medium circulating in the closed system which has been employed in an experimental turbo-machine plant utilizes a high-pressure gas intake, as illustrated in FIG. 3. The change-over behavior that can be attained by this arrangement when controlling the power output is very positive, and permits immediate load surges. Unfortunately, an auxiliary compressor is needed in order to charge the storage tank thus making the apparatus more complicated and more costly.